Multilayered packaging for greasy products

ABSTRACT

The invention relates to a multilayered packaging for greasy products or part of said packaging, comprising a carrier layer made of a polymer material as main component and at least one layer placed on said carrier layer that does not form the outer side of the packaging, said layer containing a starch derivative as main component. The invention is characterized in the starch derivative is a starch derivative modified with a C 2 –C 6 -alkylene oxide. The invention also relates to the use of a C 2 –C 6 -alkylene oxide derivatized starch as main component of a layer of a multilayered packaging, which is placed on a carrier layer made of a polymer material in said packaging with the aim of rendering said multilayered packaging grease-tight.

This application claims benefit of priority of PCT Application No.PCT/EP01/07456, filed Jun. 29, 2001 and published on Jan. 10, 2002, asWO 02/02412, and German Application Nos. 100 32 252.2, filed Jul. 3,2000, and 100 49 665.2, filed Oct. 6, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to multilayer greaseproof packaging materialshaving a carrier layer which is made of paper/cardboard or othersuitable substances on a polymer basis.

2. Description of the Related Art

It has been known for a long time to provide paper and cardboardcontainers with coatings having a barrier effect for flavors orhumidity/liquids. DE 41 09 983 A1 describes a flexible packagingcontainer comprising a composite made of a paper layer and athermoplastic layer or film. The thermoplastic layer or film materialconsists of starch, a synthetic, non-polyolefinic polymer containinghydroxyl groups, e.g. an oxygenated polymer, and softeners of naturalorigin, e.g. polyalcohols derived from starch. Said material can bemelted by supplying heat and therefore, it is extrudable. DE 41 37 802A1 proposes to laminate a cardboard with a coated paper web to obtain arottable, liquid-repellent product. The coating of the paper web shallbe effected on a starch basis, e.g. on potato starch basis. DE 42 94 110discloses a coating dispersion which is prepared from copolymers ofoxidized starch and styrene, butadiene, acrylic acid or similarpolymerizable molecules. Said dispersion reduces the gas and waterpermeability of cardboard or paper.

However, it is often necessary to provide packaging materials which havea high resistance to grease. Thus, food for animals, bread andconfectionery, sweets and chocolate require a packaging having aparticularly high resistance to grease which is for example indicated bythe so-called KIT numbers exhibiting values between 8 and 12. High KITnumbers represent high resistances to grease, values as from 6 alreadyrepresent a good resistance to grease.

Corresponding commercially offered paper/cardboard packaging has usuallybeen subjected to a grease-repellent surface and/or mass treatment. Atpresent, mainly fluoropolymers are used for said mass treatment orsurface treatment, up to 5% by weight of coating material being appliedonto the material. Grease resistances of >6 to 8 can only be obtained bycombining layer and mass treatment, grease resistances with KIT numbersof >12 cannot be guaranteed with the present systems. For example,packing dry food for animals with a low grease content (<10%) requires amass treatment of the backside, in case of higher grease contents, abarrier is realized by mass treatment in combination with a surfacecoating.

Waste paper, paperboard and cardboard packaging are regularly disposedvia the waste paper circuit. Thus, via the pulping process, the halogenpolymers used as grease barrier either arrive at the virgin paperproduct or in the waste water of the process.

Starch ethers are known as auxiliary agents and starting materials inthe paper industry. The properties used are described in detail in thepertinent literature. They are used in surface coating and coating,respectively, and in pigmented paper coatings. In accordance with theBGVV (Bundesinstitut für gesundheitlichen Verbraucherschutz undVeterinärmedizin), paper, cardboard, and paperboard admitted for foodcontact may also contain starch ethers (e.g. hydroxyethyl ether andhydroxypropyl ether). Further, starch ethers are used as a component ofadhesives because of their good film-forming property and their waterbonding capacity. Respective literature is to be found for example inUllmanns Enzyklopäidie der technischen Chemie; W. Baumann/B. Herberg:Papierchemikalien—Fakten zum Umweltschutz (Springer-Verlag); O. B:Wüirzburg: Modified Starches: Properties and Uses (CRC Press).

Further, it is known that starch ether derivatives can be processed tofoils/films from an aqueous solution, particularly using castingtechnology.

When preparing the starch ethers in accordance with the so-called Slurrymethod, the aqueous starch suspension is derivatized under alkalineconditions at temperatures of up to 50° C. The degree of substitution(DS) is substantially around 0.2. The preferred derivatization at the C₂atom is characteristic for said methods. Another method which issubstantially known from scientific examinations (autoclave method) isbased on alkaline-activated starch and realizes more homogeneousderivatizations at lower TS (i.e. dry substance) concentrations, thedegree of substitution (DS), however, being adjusted similarly.Proceeding in accordance with said strategy is described in DE 42 23 471A1, the starch ethers obtained according to this document being intendedto be used for the preparation of films, particularly for use asoverhead, copying, and printing films or for the surface finishing ofspecial papers, and as packaging material. Further, it is indicated insaid publication that the ether derivative films mentioned therein canbe used in combination with other materials.

SUMMARY OF THE INVENTION

The object of the present invention is to provide packaging materialswhich are admissible according to food law, and which are greaseproof.

Surprisingly, it was found that substrates which themselves do notprovide sufficient resistance to grease, such as paper, cardboard,paperboard, or other materials which are made of or contain cellulose,are greaseproof when coated with alkylene-oxide-derivatized starch.

Therefore, the present invention provides multilayer packagings forgreasy products or parts of said packagings, said packagings comprisinga carrier layer made of a polymer material as the main component, and atleast one layer applied onto said carrier layer and not forming theouter side of said packaging, said layer applied onto said carrier layercontaining an alkyene-oxide-derivatized starch as the main component.The alkylene oxide used for this purpose can suitably be a C₂–C₆alkylene oxide. C₂–C₄ alkylene oxides are preferred.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

By coating a carrier material with the functional layer of a “starchderivative”, a greaseproof composite system is realized. The starchcomponent is responsible for the resistance to grease and additionallyhas the property of being biologically degradable. Moreover, such astarch can be suitably incorporated into coating masses for the purposeindicated, since—in contrast to native starch—it is not susceptible tore-aggregation (retro gradation).

The packagings according to the invention are not limited to specificembodiments. An exemplary, preferred field of application comprisespackagings of foodstuffs and food for animals which simultaneously havea low water content and a high grease content, particularly foldingboxes. Respective examples are packagings for biscuits or cookies,chocolates, other sweets, dry food for animals for which a particularlygood barrier against the passage of water vapor is not required. Inaddition, packagings for fat-containing non-foods (e.g. cosmetics,oil-containing color pigments, or the like) can be embodied inaccordance with the invention.

Further possibilities of applications are the coating of polymers otherthan cellulose with the material proposed according to the invention(e.g. other packaging plastics) for similar packaging requirements.Another possible use is the coating of paper intended as a wrappingpaper.

With the packaging materials according to the present invention, highresistances to grease are realized corresponding to KIT numbers in therange of from 6, particularly at least of from 8, but usuallysubstantially higher. Thus, resistances having a KIT number of 10 or 12,in extreme cases of even more than 21, can be achieved which cannot beguaranteed with the previous, non-bio-compatible and non-bio-degradablesystems.

Further advantages of the packagings according to the invention arecompatibility of their production with usual methods of the paper andcardboard production and biological degradability; said packagings, incomparison with usual systems, being classified as particularlyadvantageous with regard to the economic and/or ecologic evaluation,particularly to the coating costs, including process costs, and thecompatibility with the paper recycling process.

Due to their bio-degradability, the packagings according to theinvention ensure a good compatibility with the recycling and waste waterpurification possibilities of waste paper disposal facilities. Thedegradation behavior in the paper circuit represents a decisiveadvantage in the sense of avoiding the introduction of additionalinterfering substances.

Particularly suitable materials for the carrier layer are paper,paperboard or cardboard, if desired in mixture with other suitablematerials or materials usual or admissible in the packaging technologyof foodstuffs, such as binders or colorants. But also other materials,preferably materials on the basis of natural polymers, such as celluloseor the like, or plastics can be used.

Starch derivatives which are suitable according to the invention arestarch derivatives which have been derivatized with an alkylene oxide,such as ethylene oxide or propylene oxide, or with a longer-chainalkylene oxide. The attached radicals enlarge the distances between themolecular chains and thus increase their mobility. The inner softeningeffect thus provided can only be undone by destroying the chemicalbonds.

The starch derivative should preferably form a continuous film on thecarrier layer. If this is the case, already very thin layers with aweight per unit area as from 6 g/m² can be greaseproof, provided thatthe carrier material has a relatively high evenness.

The coating can be provided as a surface layer of the inner side of thepackaging and/or as an intermediate layer, optionally having thefunction of an adhesive layer between paper or cardboard layers or thelike. Also several coatings applied one directly onto the other can beadvantageous. Further, a so-called prime-coating (e.g. with usual papercoating substances, like kaolin or starch) can be applied prior to thecoating with the starch derivative, said prime-coating serving thepurpose of calendering or polishing (smoothing) the surface in advance.Weights per unit area for achieving defect-free layers can thus bereduced.

The layer containing the starch derivative can optionally be placed ontothe carrier layer by applying a self-supporting layer made of thismaterial. Preferably, however, a solution or a suspension of the starchderivative is prepared using a suitable quantity of dry substance, andis applied onto the carrier material; it is preferably an aqueoussolution or a suspension. A well-suited quantity of dry substance (TS)of the starch derivative is in the range of about 5 to about 50% byweight, preferably in the range of from about 10 to about 40% by weight,the quantity to be actually selected depending on the intendedapplication method. Thus, in some cases, a quantity of down to 4% byweight may be sufficient.

The application can for example be effected with a knife (or “doctorblade”), by spraying or by roller application, also by “pressurecasting” of a more concentrated solution, and by application of athermo-plasticized melt (“extrusion”) to the surface of the carrier. Inany case, the water content of the starch derivative should be reducedto preferably <25% by weight after application onto the carrier material(e.g. by infrared or convection drying).

Besides the starch derivative, the layer to be applied onto the carrierlayer may contain additional additives. On the one hand, the addition ofpigments (as it is customary in the paper industry) offers itself, onthe other hand, glycerol, urea, borax, glyoxal or other additives havingsimilar properties and effects can be added in order to achieve desiredvalues with respect to elasticity, water stability, and long-termstability. Also, the KIT value can sometimes be influenced positively byadding such substances, e.g. by adding glycerol or curing agents (e.g.glyoxal). The proportion of starch derivative should preferably be in anamount to ensure the formation of a defect-free film.

Preferably, native starches, such as corn (maize), wheat, pea, potato,or tapioca starch, are used as starting materials.

The modification is for example effected with a C₂ or C₃ alkylene oxide.Propylene oxide is preferred.

Since the starch is suitably modified in the presence of a base,although the mass provided for the coating should advantageously reactsubstantially neutrally, which implies that normally, neutralizationwith acid has to be effected, the modified starch is usually highlycharged with salts. Advantageously, said salt content should not be toohigh, particularly when using the particularly preferred corn or wheatstarch. Therefore, it is recommended that the coating mass in theconcentration provided for the application should have a conductivity ofnot more than 4,000 to 5,000 μS/cm, preferably of <2,000 μS/cm.

The addition of acids and bases should be effected under the aspect thatthe occurring salt is generally recognized as safe with regard to foodlaw. Suitable acids are phosphoric acids, a suitable base is sodiumhydroxide. The desalination can for example be effected by dialysis.

Coatings with higher-derivatized starches present more favorable KITnumbers than those with lower degrees of derivatization. Correspondingpositive effects, however, also depend on the origin of the starch used.In accordance with the invention, the degree of derivatization is in therange of between 0.1 to 1.0, preferably of between 0.1 and 0.3.

The preparation of a starch ether solution suitable as a coatingmaterial or casting solution or the like for the present invention canfor example be effected as follows: The starch (e.g. wheat, corn,tapioca, potato, or HA pea starch, e.g. from peas) is stirred forseveral hours in approximately twice its weight of water andsubsequently roughly released from water, e.g. by sucking-off. Thestarch absorbs approximately its own weight of water, so that itcontains about 40 to 60% of dry substance. Subsequently, it isre-suspended in about 1.5 times of its wet weight and disintegrated byaddition of the same quantity of about a 10% base or sodium hydroxide.Immediately thereafter, within several minutes up to about one hour,alkylene oxide, preferably propylene oxide, in a quantity of from about25 to 75% by weight relative to the basic weight of the dry starch isadded, maintaining mild temperatures. Room temperature is well-suited.The mixture is stirred for several hours and subsequently rested forabout 20 hours; thereupon, it is neutralized with acid. In casedesalination is to be carried out, dialysis against water is for exampleused. If desired, the desalinated solution is carefully reconcentrated.

In case propylene oxide is used in a quantity of about 50% by weight,the degree of derivatization of the starches is about 0.2, in othercases it is correspondingly higher or lower.

A desalination or separation of interfering inhomogeneities can forexample also be effected by ultrafiltration. Should the concentration ofthe product be too high, a dilution with deionized water can beeffected.

After addition of possibly desired additives (e.g. preserving agents,fillers, antistatic agents, elasticity-improving agents, curing agents),a mechanical separation using filters or a centrifuge can be carriedout, if required, which simultaneously will accomplish degasification ofthe solution to be processed.

A coating solution which is particularly suitable for the purposes ofthe invention has the following rheological properties.

A dynamic viscosity of from 0.1 Pas to 40 Pas at a temperature of 25° C.and a shearing speed of 30.7 s⁻¹.

Viscoelastic properties of the polymer solution, the ratio of viscous toelastic proportion having Tan κ values of between 1 and 10 (50 atmaximum) at a temperature of 25° C. and a shearing speed of 30.7 s⁻¹.

Such values can be obtained without difficulties when using the methodmentioned as an example.

Further, the method offers the advantage that the starch is reacted andprocessed particularly carefully and continuously at relatively lowtemperatures (<60° C.) or completely at room temperature, which haspositive effects on the coating of the carrier material. Due to thesolubility in cold water after neutralization, separation, desalinationand reconcentration, the starch can be processed so carefully thatdegradation reactions do not occur at all or only to an insignificantextent.

The aqueous casting solution can preferably be applied onto the materialweb (paper) at room temperature or at slightly increased temperatures,using a suitable application system (e.g. a knife).

The use of hydroxypropyl ether starches prepared according to theautoclave method, particularly from wheat starch, corn starch, or HA peastarch, has been proven to be particularly favorable, said starchesbeing used as solutions having TS contents of from 12 to 20% by weightand degrees of derivatization (DS) of preferably from 0.1 to 1.0, morepreferably of up to 0.4. In comparison with commercial samples (coatedwith fluorocarboxylic acids), said starches show markedly betterresistances to grease, particularly also in edge portions which areparticularly critical when folding boxes are used. Compared to thepreviously mentioned coatings using commercial starch derivativesaccording to the invention, the weights per unit area used for thecoatings with said starches can be reduced.

Example: 713 g wheat starch is stirred for four hours in 1.3 1 distilledwater and subsequently filtered by sucking. The wet starch is stirred upwith 1.824 1 water and mixed with 1.811 g of 10% sodium hydroxide whichwas obtained by mixing 376 g 50% NaOH with 1.505 g water. Derivatizationis effected using 323 g propylene oxide at 23° C. which is added understirring within 20 minutes. The mixture is stirred for further 4 hoursand rested for 20 hours. Neutralization is effected with 40% phosphoricacid (about 700 g). Subsequently, the solution is filled into dialysistubes and dialyzed for about 4 days, the water being exchanged daily.The product is reconcentrated to more than 20% of dry substance using avacuum rotation evaporator.

The starch ether obtained has a degree of derivatization of about 0.2.The conductivity of the coating mass is about 1100 μS/cm.

The below-mentioned coating masses were prepared similar to said exampleand applied with a knife onto a unilaterally coated chromo duplexcardboard (GD2), 310 g/m², thickness about 420 μm. After the firstcoating had dried (finger-dry, duration about 2 h), a second layer wasapplied and dried at room temperature and at about 50% room moisture forabout 1 week or longer, if desired.

Three cardboard sheets of the coated samples were used to determine thecoated mass by weighing (according to DIN 53 104: test of paper andcardboard, determination of the weight per unit area, September 1971)and the thickness with a caliper gauge (caliper: even/bulged, 30 SKT,MB=1 μm). Further, the KIT number for nonpolar substances was determinedaccording to the 3M KIT test. Solvent mixtures from castor oil, tolueneand heptane serve as test liquids. The KIT solution which has thehighest number and stands on the sample for 15 sec. without penetratingor causing a discoloration, is the characterizing KIT number.

Derivatization Surface with PPO (in % Conductivity applica- Layer byweight (optionally tion thick- KIT- relative to the after weight nessnum- Raw material raw material) desaltation) [g/m²] [μm] ber Wheatstarch 50 1100 21.5 33.24 >21 (Kröner) 50 8180 32.6 29.6 8 75 1600 11.225 9 25 5150 31 34.8 13 25 10700 21.1 27.1 9 Corn starch 50 1800 21.534.3 15 (Cerestar) 50 6600 16.3 20.4 14 25 4400 15 25.9 14 75 1340 4.918.6 >21 Corn 50 1800 15.6 23.1 19 starch + 5% by weight glycerol Corn50 1800 16.6 34.7 15 starch + 2% by weight curing agent Potato starch 50870 21 18.7 9 Amylex 50 3700 18.1 18.4 6 20/20 (Südstärke) Tapioka 50840 8.6 221 8 starch (Cerestar) 50 12200 11.3 23 8 HA pea ~50 >16starch, 18% by weight TSMultilayer Packaging for Greasy Products

The present invention relates to a multilayer packaging for greasyproducts or part of said packaging, comprising

-   -   a carrier layer made of a polymer material as the main        component, and    -   at least one layer applied onto said carrier layer and not        forming the outer side of said packaging, said layer containing        a starch derivative as the main component,        characterized in that said starch derivative is a starch        derivative modified with a C₂–C₆ alkylene oxide. The invention        further relates to the use of a starch derivatized with a C₂–C₆        alkylene oxide as the main component of a layer of a multilayer        packaging said layer being applied onto a carrier layer of said        packaging which is made of a polymer material, with the aim of        rendering said multilayer packaging greaseproof.

1. A multilayer packaging for greasy products or part of said packaging,comprising a carrier layer made of a polymer material as the maincomponent, and at least one layer applied onto said carrier layer andproviding one of a surface layer of an inner side of said multilayerpackaging and an intermediate layer of said multilayer packaging,wherein the at least one layer applied onto said carrier layer (a)contains a starch derivative as the main component, wherein said starchderivative is a starch derivative modified with a C₂–C₆ alkylene oxideand has a degree of derivatization of from 0.1 to
 1. and (b) has beenapplied from a coating solution having a dynamic viscosity of from 0.1Pas to 40 Pas at a temperature of 25° C.
 2. The multilayer packaging ofclaim 1, wherein said starch derivative is a starch derivative modifiedwith a C₂–C₄ alkylene oxide.
 3. The multilayer packaging or part of saidpackaging of claim 1, wherein said C₂–C₆ alkylene oxide is propyleneoxide.
 4. The multilayer packaging or part of said packaging of claim 1,wherein said starch derivative was obtained by modification of corn,wheat, potato, HA pea, or tapioca starch.
 5. The multilayer packaging orpart of said packaging of claim 1, wherein said starch derivative has adegree of derivatization of from 0.2 to 0.3.
 6. The multilayer packagingor part of said packaging of claim 1, wherein said polymer material ofsaid carrier layer is a polymer occurring in nature.
 7. The multilayerpackaging or part of said packaging in accordance with claim 1, whereinsaid layer containing a starch derivative as the main component containsadditional components selected from among pigments, softeners, agentsincreasing the long-term stability, agents increasing the waterstability, and agents affecting the elasticity.
 8. The multilayerpackaging or part of said packaging, of claim 4, wherein additionalcomponents are selected from among glycerol, urea, borax or glyoxal. 9.Use of a starch derivative, modified with a C₂–C₆ alkylene oxide as themain component of a layer of a multilayer packaging, said layer beingapplied from a coating solution having a dynamic viscosity of from 0.1to 40 Pas at a temperature of 25 ° C. onto a carrier layer of saidpackaging, the carrier layer being made of a polymer material, so as toobtain a greaseproof multilayer packaging.
 10. Use in accordance withclaim 9, wherein said C₂–C₆ alkylene oxide is propylene oxide.
 11. Usein accordance with any of claims 9 and 10, wherein said starchderivative was obtained by modification of optionally partly degradedcorn, wheat, potato, HA pea, or tapioka starch and has a degree ofderivatization of from 0.1 to 0.4.
 12. Use in accordance with any ofclaims 9 to 11, wherein said layer contains additional componentsselected from among pigments, softeners, agents increasing the long-termstability, agents increasing the water stability, agents increasing theKIT value, and agents affecting the elasticity, preferably selected fromamong glycerol, urea, borax, or glyoxal.
 13. The multilayer packaging orpart of said packaging of claim 4, wherein said starch derivative wasobtained by modification of corn, wheat, potato, HA pea, or tapiocastarch, and wherein said corn, wheat, potato, HA pea, or tapioca starchare partly degraded.
 14. The multilayer packaging or part of saidpackaging of claim 6, wherein said polymer material of said carrierlayer is cellulose.
 15. The multilayer packaging of claim 1, wherein theat least one layer applied onto said carrier layer has been applied froma coating solution having a conductivity of not more than 5,000 μS/cm.